Methods for manufacturing organic LEDs are classified broadly into the categories vacuum deposition methods and application methods. Among those methods, the application methods have advantages such as easy deposition for large areas and high material use efficiencies. In order to use the application methods, there is a need to reduce the numbers of layers in organic LEDs, and the light-emitting layers are required to have a single layer.
Conventionally, as an organic white light-emitting element including a single light-emitting layer, PLT 1 reports a single-layer type white light-emitting organic EL element with an inserted single light-emitting layer composed of a composition containing at least (a) a polymer and (b) luminescent center forming compounds, which is characterized in that the composition contains therein an electron transporting substance and a hole transporting substance in a balanced manner, the polymer itself produces a luminescent color of a blue or a shorter wavelength, two or more of the luminescent center forming compounds are dispersed as molecules in the polymer, the respective luminescent center forming compounds each independently produce luminescence, and two or more of the luminescent center forming compounds are used in combination so that as the luminescent color as a whole of the organic EL element appears as white light. Other documents include PLTs 2 to 4.
Methods for manufacturing organic LEDs are classified broadly into the categories vacuum deposition methods and application methods. Among those methods, the application methods have advantages such as easy deposition for large areas and high material use efficiencies. Methods for obtaining white light source devices by the application methods include: (1) a method of placing, on a plane surface, organic light-emitting elements that emit light respectively in blue, green, and red; (2) a method of stacking light-emitting layers that emit light respectively in blue, green, and red; and (3) a method of providing one light-emitting layer that emits light in respective colors of blue, green, and red.
PLT 5 discloses an organic light-emitting element that has a light-emitting layer containing a phosphorescent dopant material doped in an inactive host substance and a charge transporting dopant for doping, and can efficiently emit light in a blue region of a visible spectrum.